diff --git a/src/cmd/compile/internal/types2/named.go b/src/cmd/compile/internal/types2/named.go
index 834a25066b..3ba53052d7 100644
--- a/src/cmd/compile/internal/types2/named.go
+++ b/src/cmd/compile/internal/types2/named.go
@@ -113,6 +113,9 @@ func (t *Named) SetUnderlying(underlying Type) {
 		panic("underlying type must not be *Named")
 	}
 	t.resolve(nil).underlying = underlying
+	if t.fromRHS == nil {
+		t.fromRHS = underlying // for cycle detection
+	}
 }
 
 // AddMethod adds method m unless it is already in the method list.
diff --git a/src/go/types/named.go b/src/go/types/named.go
index 6c77146485..f0c22d29e3 100644
--- a/src/go/types/named.go
+++ b/src/go/types/named.go
@@ -115,6 +115,9 @@ func (t *Named) SetUnderlying(underlying Type) {
 		panic("underlying type must not be *Named")
 	}
 	t.resolve(nil).underlying = underlying
+	if t.fromRHS == nil {
+		t.fromRHS = underlying // for cycle detection
+	}
 }
 
 // AddMethod adds method m unless it is already in the method list.